                    [:lbf :N]                  4.44822
                    [:m :ft]                   3.28084
                    [:kg :lb]                  2.20462262185
+                   [:hp :W]                   745.69987158227022
                    [:psi :kPa]                6.894757293168361
                    [:lb-per-gal :kg-per-m3]   119.826
                    ;; slurry rate conversion not needed (use [:bbl :m3])

(def rand-force-unit (rand-unit :force))
(def rand-length-unit (rand-unit :length))
(def rand-mass-unit (rand-unit :mass))
(def rand-pressure-unit (rand-unit :pressure))
(def rand-proppant-concentration-unit (rand-unit :proppant-concentration))
(def rand-slurry-rate-unit (rand-unit :slurry-rate))

                   [:kg-per-m3 :lb-per-cu-ft] #(/ % (factors [:lb-per-cu-ft :kg-per-m3]))
                   [:ft-lb :J]                #(* % (factors [:ft-lb :J]))
                   [:J :ft-lb]                #(/ % (factors [:ft-lb :J]))
                   [:lbf :W]                  #(* % (factors [:lbf :W]))
                   [:W :lbf]                  #(/ % (factors [:lbf :W]))
                   [:ft :m]                   #(/ % (factors [:m :ft]))
                   [:m :ft]                   #(* % (factors [:m :ft]))
                   [:kg :lb]                  #(* % (factors [:kg :lb]))
                   [:lb :kg]                  #(/ % (factors [:kg :lb]))
                   [:hp :W]                   #(* % (factors [:hp :W]))
                   [:W :hp]                   #(/ % (factors [:hp :W]))
                   [:psi :kPa]                #(* % (factors [:psi :kPa]))
                   [:kPa :psi]                #(/ % (factors [:psi :kPa]))
                   [:lb-per-gal :kg-per-m3]   #(* % (factors [:lb-per-gal :kg-per-m3]))
